reverse the rotation of a object

Question

In my swift code func rotate rotates a football. In leftB I want to reverse the rotation of the football. Currently the rotation is going clockwise. If leftB is hit I want the rotation direction to be reversed from the same location.

    func Rotate() {
  
        self.rotation = UIViewPropertyAnimator(duration: 10, curve: .linear, animations: {
            self.football.transform = self.football.transform.rotated(by: CGFloat.pi)
        })

        self.rotation?.addCompletion { [weak self] (_) in
            self?.Rotate()
        }

        self.rotation?.startAnimation()


}


@objc func leftB() {
}

Answer 1

If you use a rotation angle of π, the system can't tell if it's supposed to rotate clockwise or counter-clockwise. That's because rotating by π represents a 180 degree rotation, and you could do that by going clockwise or counter-clockwise. Use rotation changes of π/2 or -π/2.

Here is some code that works, from a little sample project I slapped together to demonstrate how to make it work:

    enum RotationDirection: Int {
        case clockwise
        case counterclockwise
    }
    
    @IBAction func doRotate(_ sender: UIButton) {
        defer {
            let buttonTitle = isRotating ? "Stop rotating" : "Rotate"
            sender.setTitle(buttonTitle, for: .normal)
        }
        if isRotating  {
            isRotating = false
        } else {
            isRotating = true
            rotate()
        }
    }
    
    func rotate() {
        
        guard isRotating else { return }
        
        let rotationAngle = rotationDirectionControl.selectedSegmentIndex == RotationDirection.clockwise.rawValue ? CGFloat.pi/2 : -CGFloat.pi/2
        self.rotation = UIViewPropertyAnimator(duration: 0.5, curve: .linear, animations: {
            self.football.transform = self.football.transform.rotated(by: rotationAngle)
        })
        
        self.rotation?.addCompletion { [weak self] (_) in
            self?.rotate()
        }
        self.rotation?.startAnimation()
    }

Edit:

You can download a sample project using the above code here.

(I animated a UILabel whose outlet I named "football." Yours is probably a UIImage.)